Method and apparatus providing out of band validation by content analysis in a cable TV network

ABSTRACT

A method and test instrument for validating one or more out of band (OOB) channels in a CATV network, particularly one having a Remote PHY architecture. The method and test instrument may quickly and efficiently determine if an OOB channel is carrying valid data and is therefore “active.”

BACKGROUND

The cable space is rapidly embracing the Remote PHY (also known asR-PHY, R PHY, and RPHY) network architecture. Remote PHY is popularamong cable television (CATV) network service providers because it doesan effective job of alleviating the rack space, power, and coolingconstraints in the hub of the network. Remote PHY does this byseparating out the PHY layer and redistributing it out to the fibernode. Remote PHY specifications exist and have become the standard forthe industry.

Remote PHY is part of a larger family of technologies known asdistributed access architectures (DAA), which alleviate congestion inthe hub. In general, DAA technologies such as Remote PHY virtualize andmove certain aspects of a network out of the hub and closer tosubscribers. Hubs are evolving from housing row after row of specializedequipment and RF splitting/combining networks, into potentially littlemore than a small collection of optical switches and routers.

In addition to reducing space, power and cooling requirements in thehub, Remote PHY also eliminates the analog optical link and replaces itwith a commodity digital 10G Ethernet link. This provides distinctadvantages such as e.g., 1) a digital link is easier to set up, takingless time to deploy; 2) the link is more reliable, requiring lessmaintenance and manpower in the future; and 3) significant signal tonoise ratio (SNR) gains may be achieved using digital optical linksversus the old amplitude modulated links, potentially enabling highermodulation orders for DOCSIS (Data Over Cable Service InterfaceSpecification) 3.1 downstreams. Technologies such as Remote PHY andDOCSIS 3.1 are extending the life of the hybrid fiber coax (HFC) plantby leveraging much of the existing infrastructure to deliver Gigabitspeeds.

In the traditional network architecture, all of the RF is generated orreceived in a headend or hubsite. This provides a centralized placewhere tests can be performed. If the content of the signals is ensuredin the headend/hubsite then the measurements out in the field reallyonly need to validate the physical layer integrity to ensure that theappropriate content is reaching the end user. The Remote PHY networkarchitecture changes this. In this environment, the RF signals are nolonger generated in a centralized place, but rather the creation isdistributed out closer to the network edge; typically at the node. Thisrequires that the testing is also performed out at the node to ensurethat the signals are correct.

FIG. 1 illustrates an example CATV network 10 having a Remote PHYarchitecture. Specifically, the network 10 includes a converged cableaccess platform (CCAP) device 12, switch/router 14, Remote PHY device(RPD) 16 and a set-top box 18. In the illustrated example, a user'stelevision 20 is connected to the set-top box 18 to display video 30that may include broadcast audio and video 32 (e.g., programs) and auser guide based on guide data 34. In the illustrated example,configuration data 22 is used to configure the CCAP device 12,switch/router 14, and RPD 16. Data 28, which may include InternetProtocol (IP) data 26 and or voice over IP (VoIP) data 28 may bereceived by the CCAP device 12.

In the illustrated example, the network 10 may utilize QAM (quadratureamplitude modulation) and MPEG (Moving Picture Experts Group) transportstreams to deliver the data 24 and video 30 to the RPD 16 through one ormore Ethernet connections E1-E5 and deliver the data 24 and video 30 tothe set-top box 18 from the RPD 16 through e.g., a coaxial connectionC1. It should be appreciated that the switch/router 14 may not berequired, meaning that the CCAP device 12 could be connected directly tothe RPD 16, if desired. The network 10 may also transmit certaininformation (e.g., control, guide data) in one or more out of band (OBB)channels, typically used by the set-top box 18.

As can be seen, there are many network elements must be configuredproperly for the guide data 34 to be delivered and correctly modulatedinto the out of band channel. If any one component is misconfigured ornot functioning properly the resulting OOB RF channel may contain onlyfiller data and will therefore be unusable by the set-top boxes 18.Accordingly, there is a need and desire for a test that can quickly andaccurately determine if an OOB channel is carrying valid data and istherefore “active.”

SUMMARY

Embodiments described herein may include a method and test instrumentfor validating one or more out of band (OOB) channels in a CATV network,particularly one having a Remote PHY architecture. For example, theembodiments described herein may be configured to quickly andefficiently determine if an OOB channel is carrying valid data and istherefore “active.”

In one embodiment, a computer-implemented method is provided. The methodis performed on a test instrument adapted to test an out of band (OOB)channel in a downstream portion of a cable television network having aRemote PHY architecture. The method comprises: demodulating the capturedOOB channel data; extracting OOB content from the demodulated OOBchannel data; determining whether the OOB content includes apredetermined amount of valid data; and determining that the OOB channelis active when it is determined that the OOB content includes thepredetermined amount of valid data.

In another embodiment, a test instrument for testing an out of band(OOB) channel in a downstream portion of a cable television networkhaving a Remote PHY architecture is provided. The test instrumentcomprises a storage device; and a processor executing programinstructions stored in the storage device and being configured tocapture OOB channel data transmitted in the downstream portion of thenetwork; demodulate the captured OOB channel data; extract OOB contentfrom the demodulated OOB channel data; determine whether the OOB contentincludes a predetermined amount of valid data; and determine that theOOB channel is active when it is determined that the OOB contentincludes the predetermined amount of valid data.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an example CATV network having a Remote PHY architecture.

FIG. 2 shows the example CATV network of FIG. 1 being tested by a testinstrument in accordance with the disclosed principles.

FIG. 3 shows an example method of validating one or more out of band(OOB) channels in accordance with the disclosed principles.

FIG. 4 shows an example user interface that may be output during themethod illustrated in FIG. 3 .

FIG. 5 shows a test instrument for validating one or more out of band(OOB) channels in accordance with the disclosed principles.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

The disclosed principles provide a method and test instrument forvalidating one or more out of band (OOB) channels in a CATV network,particularly one having a Remote PHY architecture. In one or moreembodiments, the disclosed method and test instrument may combine a fullsoftware demodulation and extraction of transport layer data with ananalysis of said transport layer to determine if an OOB RF channel is“active” (i.e., actually carrying valid data) or not (i.e., simplystuffed with filler data to maintain the required constant bitratetransmission).

For example, FIG. 2 shows the CATV network 10 of FIG. 1 being tested bya test instrument 100 in accordance with the disclosed principles. Inthe illustrated embodiment, the test instrument 100 is connected on theRemote PHY side of the network (e.g., at the RPD device 16, the user'spremises, etc.) and will capture, among other things, out of band (OOB)channel data 110 transmitted in the downstream direction over e.g., thecoaxial connection C1. In one or more embodiments the OOB channel data110 is collected by the test instrument 100, which may analyze the datato verify its contents to determine if the OOB channel or channels areactive (i.e., carrying valid data) or not (i.e., simply stuffed withfiller data to maintain the required constant bitrate transmission).This is a feature that is not currently being done by test instrumentsand thus provides a huge advantage in the technical field.

FIG. 3 shows an example method 200 of validating one or more OOBchannels in accordance with the disclosed principles. In one or moreembodiments, the method is performed by the test instrument 100. In oneembodiment, the test instrument 100 is one of the OneExpert CATV line ofanalysis meters manufactured and sold by VIAVI Solutions Inc. that ismodified to perform the method 200 and other processing disclosedherein. In one or more embodiments, the modifications can be made to theOneExpert analysis meter by a software/firmware upgrade. In oneembodiment, the method 200 may be activated by a technician andperformed as part of an “OOB Channel Check” feature or other feature(e.g., “OneCheck”) performed by the test instrument 100. The method 200may be activated using one or more buttons or a touchscreen includedwith the instrument 100 (described below in more detail with respect toFIG. 5 ). Regardless of how it is activated, the method 200 should beexecuted after the test instrument 100 is connected to a tap on theRemote PHY side of the network 10.

At step 202, the test instrument 100 captures OOB channel datatransported downstream (e.g., to a customer's premises). At step 204,the captured OOB channel is, among other things, demodulated so that thetest instrument 100 can extract and subsequently analyze the contents ofthe data transmitted to the set-top box 18 in the OOB channel(s). As isknown in the art, there are different approaches to passing OOB signalsthrough a Remote PHY device. Two specifications referred to as SCTE(Society of Cable and Telecommunications Engineers) 55-1 and SCTE 55-2govern two of these approaches for existing legacy devices. Eachspecification outlines how the OOB data is transported. For example,SCTE 55-1 mandates that the data be transmitted in the downstreamdirection using MPEG transport streams. SCTE 55-2, on the other hand,mandates that the data be transmitted in the downstream direction usingasynchronous transfer mode (ATM) cells (referred to herein as a “streamof ATM cells”).

Each specification also describes how the data is formatted andmodulated in the downstream direction. For example, SCTE 55-1 has aphysical layer whereby the data undergoes QPSK (quadrature phase shiftkeying)/differential encoding, interleaving, reed-solomon encoding andrandomization in a specified manner to create a MAC (medium accesscontrol) sublayer having MAC packets and the MPEG transport stream as isknown in the art. In contrast, SCTE 55-2 has a link/physical layer tocreate SL-ESF (signaling link extended superframe format) frame payloadstructures having an SL-ESF format whereby the data undergoesQPSK/differential encoding, interleaving, reed-solomon encoding, andrandomization in a specified manner to create the stream of ATM cells asis known in the art. Thus, the manner in which the “demodulation” atstep 204 is performed will be specification specific and the result ofstep 204 is referred to herein as “demodulated OOB data.”

At step 206, the test instrument 100 will extract the OOB content to beanalyzed (e.g., MPEG transport stream data, ATM cell data) from thedemodulated OOB data. Since each specification uses different formatsand data structures, the OOB content to be extracted and step 206 willalso be specification specific. For example, an MPEG transport streampacket has a packet size of 188 bytes containing a four byte headerfollowed by 184 bytes of data payload. ATM cells, on the other hand, are53 bytes long and have 40 bits of header and 384 bits of payload.

The headers can be used to “lock” onto the MPEG transport stream/streamof ATM cells prior to data extraction and analysis. For example, for theMPEG transport stream, the synchronization portion of the packet headermay be detected and the test instrument 100 may ensure that it detectsadditional packets every 188 bytes. If it does, the test instrument 100has locked onto the MPEG transport stream data and the method 200 maycontinue. Likewise, for ATM cells, the detection of the Frame AlignmentSignal (FAS) within the SL-ESF framing structure may be used todetermine “sync lock.” Then, the test instrument 100 may ensure that itdetects additional packets every 53 bytes. If it does, the testinstrument 100 has locked onto the ATM cell data and the method 200 maycontinue. If the test instrument 100 cannot lock on to the MPEG streamor stream of ATM cells, the method 200 may output an alert (e.g.,audible, visual, haptic, etc.) so that the technician knows that thereis an error. At this point, the method 200 may terminate.

At step 208, the test instrument 100 may analyze the extracted OOBcontent (i.e., MPEG transport stream packets/ATM cells) to determine ifthe OOB channel is “active” (e.g., carrying valid data) or not (e.g.,carrying filler or no data). For example, MPEG transport stream packetsare identified by a packet identifier (PID). As is known in the art, apacket having a PID of 8191, is a NULL packet. In accordance with thedisclosed principles, NULL packets are not packets having valid data atstep 208 (i.e., they are considered to contain invalid data). In one ormore embodiments, the number of packets comprising valid data (i.e.,packets having non-NULL data) is compared to the number of analyzedpackets. In one or more embodiments, if the ratio of packets havingvalid data to overall packets is greater than a predetermined threshold,then the OOB channel is determined to be active. Otherwise, the OOBchannel is determined to be inactive. In one or more embodiments, thethreshold can be at least 25%. It should be appreciated, however, thatthe threshold could be higher, requiring a larger percentage of packetswith valid data to be received on the OOB channel, or lower, requiring alower percentage of packets with valid data to be received on the OOBchannel, and may be application/network specific.

In one or more embodiments, the number of packets having valid data(i.e., packets having non-NULL data) is compared to the number ofpackets having invalid data (i.e., packets having NULL data). In one ormore embodiments, if the ratio of packets having valid data to packetshaving invalid data is greater than a predetermined threshold, then theOOB channel is determined to be active. Otherwise, the OOB channel isdetermined to be inactive. In one or more embodiments, the threshold canbe at least 50%. It should be appreciated, however, that the thresholdcould be higher, requiring a larger percentage of packets with validdata to be received on the OOB channel, or lower, requiring a lowerpercentage of packets with valid data to be received on the OOB channel,and may be application/network specific.

For an SCTE 55-2 configuration, the test instrument 100 must analyze theATM cell data to determine if the OOB channel is “active” or not. Forexample, ATM cells may contain data or they may be unassigned. Inaccordance with the disclosed principles, an unassigned ATM cell isconsidered to not contain valid data at step 208 (i.e., it is consideredto contain invalid data). In one or more embodiments, the number of ATMcells with data is compared to the number of analyzed ATM cells. In oneor more embodiments, if the ratio of ATM cells having data to overallATM cells analyzed is greater than a predetermined threshold, then theOOB channel is determined to be active. Otherwise, the OOB channel isdetermined to be inactive. In one or more embodiments, the threshold canbe at least 25%. It should be appreciated, however, that the thresholdcould be higher, requiring a larger percentage of ATM cells with data tobe received on the OOB channel, or lower, requiring a lower percentageof ATM cells with data to be received on the OOB channel, and may beapplication/network specific.

In one or more embodiments, the number of ATM cells with data iscompared to the number of unassigned ATM cells. In one or moreembodiments, if the ratio of ATM cells having data to unassigned ATMcells is greater than a predetermined threshold, then the OOB channel isdetermined to be active. Otherwise, the OOB channel is determined to beinactive. In one or more embodiments, the threshold can be at least 50%.It should be appreciated, however, that the threshold could be higher,requiring a larger percentage of ATM cells with valid data to bereceived on the OOB channel, or lower, requiring a lower percentage ofATM cells with valid data to be received on the OOB channel, and may beapplication/network specific.

At this point, the OOB channel is either validated (i.e., determined tobe active) or not validated (i.e., determined to be inactive). Thus, atstep 210, the test instrument may provide an appropriate indication ofthe result of the OOB channel check. For example, the test instrument100 can provide one or more visual, audio and or haptic indicationsalerting the technician that the OOB channel validation has beencompleted. These indications can also include a result of the validation(i.e., channel active or inactive), a listing of packets/ATM cellsanalyzed, packets with valid data/ATM cells with data, and or packetswith NULL data/unassigned ATM cells that were used to determine if oneor more OOB channels were active or not. As with other indicationsprovided by the test instrument 100, there is no limit or restrictionson the type of indication used at step 210.

FIG. 4 shows an example user interface 300 that may be output by thetest instrument 100 during the method 200 illustrated in FIG. 3 . In theillustrated example, it is presumed that the user/technician hasnavigated the appropriate test instrument function keys, menu items andor soft keys to an “OOB Channel Check function” as indicated by field302. In the illustrated example, the user interface 300 includesmultiple columns 304, 306, 308, 310 and rows 320, 330, 340 describingand or outputting certain aspects of the OOB channel check function.

For example, the first column 304 is used to identify the frequency ofthe OOB channel(s) tested. Row 320 includes the label “Freq (MHz)” incolumn 304, row 330 shows a first OOB channel that was tested and thathas a 73.250 MHz frequency and row 340 shows a second OOB channel thatwas tested and that has a 104.250 MHz frequency.

In the illustrated example, the second column 306 is used to identifywhether the test instrument 100 was able to “lock” on to the MPEGtransport stream (e.g., for a set-top box following SCTE 55-1) or ATMcells (e.g., fora set-top box following SCTE 55-2). In this example, row320 includes the label “Lock” in column 306. As noted above with respectto step 206 of method 200, the inability to lock on to the MPEGtransport stream or ATM cells may result in the method 200 beingterminated without reaching the validation step (step 208), which is anerror that should be reported to the technician. In the illustratedexample, rows 330 and 340 indicate that the test instrument 100 was ableto lock on to the MPEG transport stream or ATM cells by displaying thetext “YES” in column 306. It should be appreciated that if the testinstrument 100 could not lock on to the MPEG transport stream or ATMcells, a “NO” would appear in row 330 and or row 340.

In the illustrated example, the third column 308 is used to identify thesignal-to-noise ratio (SNR) of the OOB channel(s) tested. Row 320includes the label “SNR (dB)” in column 308, row 330 shows that thefirst OOB channel has a signal-to-noise ratio of 30.1 dB and row 340shows that the second OOB channel has a signal-to-noise ratio of 29.7dB.

In the illustrated example, the fourth column 310 is used to indicatewhether the test instrument 100 determined the OOB channel(s) to beactive or not. This is indicated by row 320, which includes the label“Status” in column 310. Row 330 shows that the first OOB channel wasdetermined to be active via the label “ACTIVE.” Similarly, row 340 showsthat the second OOB channel was determined to be active via the label“ACTIVE.” It should be appreciated that if the test instrument 100determined the OOB channel(s) to be inactive, the label “INACTIVE” wouldappear in row 330 and or row 340.

It should be appreciated that the user interface could include otherinformation, if desired. For example with respect to an SCTE 55-1configuration, the user interface 300 could include fields listing thenumber of MPEG packets analyzed during the test, the number of packetswith valid data, and or the number of packets with NULL data, to name afew. With respect to an SCTE 55-2 configuration, the user interface 300could include fields listing the number of ATM cells analyzed during thetest, the number of ATM cells with data, and or the number of unassignedATM cells, to name a few.

FIG. 5 shows a high-level block diagram of the test instrument 100,according to an example embodiment. It should be appreciated that thetest instrument 100 may include components other than those shown. Thetest instrument 100 may include one or more ports 603 for connecting thetest instrument 100 to a tap within the network 10 shown in FIG. 2 . Theone or more ports 603 may include connectors for connecting to cables inthe network that carry traffic for upstream and downstream channels. Thetraffic may include the MPEG stream and packets (or ATM cells) discussedherein as well as other data. The test instrument 100 may include atelemetry interface 604 for connecting to a telemetry channel, such as aWiFi interface, Bluetooth interface, cellular interface or anothernetwork interface. The test instrument 100 may connect to a remotedevice via the telemetry interface 604.

The test instrument 100 may include a user interface, which may includea keypad 605 and display 613. The display 613 may include a touch screendisplay. A user may interact with the test instrument 100, such as toenter information, select operations, view measurements, view outcomesof the 00B channel validations disclosed herein, via the user interface.

A data storage 651 may store any information used by the test instrument100 and may include memory or another type of known data storage device.The data storage 651 may store measured signal data, MPEG (or ATM cells)and or other content or data used by the test instrument 100,particularly the data required for method 200. The data storage 651 mayinclude a non-transitory computer readable medium storingmachine-readable instructions executable by processing circuit 650 toperform operations of the test instrument 100 such as those describedfor method 200.

Transmission circuit 641 may include a circuit for sending test signalsupstream to perform various tests, such as frequency sweep tests. Thetransmission circuit 641 may include encoders, modulators, and otherknown component for transmitting signals within the network. Receivercircuit 642 may include components for receiving signals from thenetwork. The components may include components such as a demodulator,decoder, analog-to-digital converters, and other known componentssuitable for a receiver circuit.

Processing circuit 650 may include any suitable hardware to perform theoperations of the test instrument 100 described herein, including theoperations described with respect to FIGS. 3-4 and method 200 describedherein. The hardware of the test instrument 100, including theprocessing circuit 650, may include a hardware processor,microcontroller, a digital signal processor (DSP), an applicationspecific integrated circuit (ASIC), a field programmable gate array(FPGA) or other programmable logic device, discrete gate or transistorlogic, discrete hardware components, or any combination thereof designedto perform the functions and methods described herein. In an example,one or more of the functions and operations of the test instrument 100described herein may be performed by the processing circuit 650 or otherhardware executing machine readable instructions stored in anon-transitory computer readable medium, which may comprise RAM (randomaccess memory), ROM (read only memory), EPROM (erasable, programmableROM), EEPROM (electrically erasable, programmable ROM), hard drives,flash memory, or other types of storage devices, which may be volatileand/or nonvolatile.

The method 200 and test instrument 100 disclosed herein providesnumerous advantages over the current state of the art. In particular,the discloses principles allow a handheld field instrument to validateone or more OOB channels in a CATV network, particularly one having aRemote PHY architecture. This analysis is simply not performed out inthe field; attempts to do so without the disclosed method and testinstrument would require running a drop from the RPD 16 to a truck andusing lab/bench type equipment out in the field. This process would becumbersome, expensive and would take a large amount of time, all ofwhich are undesirable. As such, method 200 and test instrument 100disclosed herein provide a technical solution to a technical problem,particularly in the CATV network and analysis fields.

In addition, no additional hardware is needed to carry out the method200 disclosed herein—i.e., no additional hardware is required to modifythe test instrument's hardware or the network Remote Phy architecture.In one or more embodiments, the method 200 may be ported to pre-existingtest instruments as part of a software upgrade. No board spin oradditional product cost would be required to implement the disclosedprinciples. This means that the disclosed principles may be deployed ontens of thousands of test instruments that are already deployed in thefield.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example and notlimitation. It will be apparent to persons skilled in the relevantart(s) that various changes in form and detail can be made thereinwithout departing from the spirit and scope. In fact, after reading theabove description, it will be apparent to one skilled in the relevantart(s) how to implement alternative embodiments. For example, othersteps may be provided, or steps may be eliminated, from the describedflows, and other components may be added to, or removed from, thedescribed systems. Accordingly, other implementations are within thescope of the following claims.

In addition, it should be understood that any figures which highlightthe functionality and advantages are presented for example purposesonly. The disclosed methodology and system are each sufficientlyflexible and configurable such that they may be utilized in ways otherthan that shown.

Although the term “at least one” may often be used in the specification,claims and drawings, the terms “a”, “an”, “the”, “said”, etc. alsosignify “at least one” or “the at least one” in the specification,claims and drawings.

Finally, it is the applicant's intent that only claims that include theexpress language “means for” or “step for” be interpreted under 35U.S.C. 112(f). Claims that do not expressly include the phrase “meansfor” or “step for” are not to be interpreted under 35 U.S.C. 112(f).

What is claimed is:
 1. A method performed on a test instrument adaptedto test an out of band (OOB) channel in a downstream portion of a cabletelevision network having a Remote PHY architecture, said methodcomprising: capturing, by the test instrument, OOB channel datatransmitted in the downstream portion of the network; demodulating, bythe test instrument, the captured OOB channel data; extracting, by thetest instrument, OOB content from the demodulated OOB channel data;determining, by the test instrument, whether the OOB content includes apredetermined amount of valid data based on a detected packet identifieror includes filler data to maintain a constant bitrate transmission;determining, by the test instrument, that the OOB channel is active inresponse to determining that the OOB content includes the predeterminedamount of valid data; and determining, by the test instrument, that theOOB channel is inactive in response to determining that the OOB contentincludes the filler data to maintain the constant bitrate transmission.2. The method of claim 1, wherein the OOB channel data is transmittedusing a Moving Picture Experts Group (MPEG) transport stream formattedand modulated in accordance with a Society of Cable andTelecommunications Engineers (SCTE) 55-1 specification and demodulatingthe captured OOB channel data comprises demodulating the MPEG transportstream to obtain a demodulated MPEG transport stream.
 3. The method ofclaim 2, wherein extracting the OOB content from the demodulated OOBchannel data comprises: extracting, by the test instrument, MPEG packetsfrom the demodulated MPEG transport stream.
 4. The method of claim 3,wherein determining that the OOB content includes the predeterminedamount of valid data comprises: detecting, by the test instrument, atleast one packet identifier of packets within the extracted MPEGpackets; counting, by the test instrument, a number of packetidentifiers associated with valid data; and determining, by the testinstrument, that a ratio of the number of packet identifiers associatedwith valid data to a number of packets extracted from the MPEG transportstream is greater than a predetermined threshold.
 5. The method of claim3, wherein determining that the OOB content includes the predeterminedamount of valid data comprises: detecting, by the test instrument, atleast one packet identifier of packets within the extracted MPEGpackets; counting, by the test instrument, a number of packetidentifiers associated with valid data; counting, by the testinstrument, a number of packet identifiers associated with invalid data;and determining, by the test instrument, that a ratio of the number ofpacket identifiers associated with valid data to the number of packetidentifiers associated with invalid data is greater than a predeterminedthreshold.
 6. The method of claim 1, wherein the OOB channel data istransmitted using a stream of asynchronous transfer mode (ATM) cellsformatted and modulated in accordance with a Society of Cable andTelecommunications Engineers (SCTE) 55-2 specification and demodulatingthe captured OOB channel data comprises demodulating the stream of ATMcells to obtain a demodulated stream of ATM cells.
 7. The method ofclaim 6, wherein extracting the OOB content from the demodulated OOBchannel data comprises: extracting, by the test instrument, ATM cellsfrom the demodulated stream of ATM cells.
 8. The method of claim 7,wherein determining that the OOB content includes the predeterminedamount of valid data comprises: counting, by the test instrument, anumber of ATM cells comprising data within the extracted ATM cells; anddetermining, by the test instrument, that a ratio of the number of ATMcells comprising data to a number of ATM cells extracted from the streamof ATM cells is greater than a predetermined threshold.
 9. The method ofclaim 7, wherein determining that the OOB content includes thepredetermined amount of valid data comprises: counting, by the testinstrument, a number of ATM cells comprising data within the extractedATM cells; counting, by the test instrument, a number of unassigned ATMcells within the extracted ATM cells; and determining, by the testinstrument, that a ratio of the number of ATM cells comprising data tothe number of unassigned ATM cells is greater than a predeterminedthreshold.
 10. The method of claim 1, further comprising determiningthat the OOB channel is not active when it is determined that the OOBcontent does not include the predetermined amount of valid data.
 11. Atest instrument for testing an out of band (OOB) channel in a downstreamportion of a cable television network having a Remote PHY architecture,said test instrument comprising: a storage device; and a processorexecuting program instructions stored in the storage device and beingconfigured to: capture OOB channel data transmitted in the downstreamportion of the network; demodulate the captured OOB channel data; OOBcontent from the demodulated OOB channel data; determine whether the OOBcontent includes a predetermined amount of valid data based on adetected packet identifier or includes filler data to maintain aconstant bitrate transmission; determine that the OOB channel is activein response to determining that the OOB content includes thepredetermined amount of valid data; and determine that the OOB channelis inactive in response to determining that the OOB content includes thefiller data to maintain the constant bitrate transmission.
 12. The testinstrument of claim 11, wherein the OOB channel data is transmittedusing a Moving Picture Experts Group (MPEG) transport stream formattedand modulated in accordance with a Society of Cable andTelecommunications Engineers (SCTE) 55-1 specification and the processordemodulates the captured OOB channel data by demodulating the MPEGtransport stream to obtain a demodulated MPEG transport stream.
 13. Thetest instrument of claim 12, wherein the processor extracts the OOBcontent from the demodulated OOB channel data by: extracting MPEGpackets from the demodulated MPEG transport stream.
 14. The testinstrument of claim 13, wherein the processor determines that the OOBcontent includes the predetermined amount of valid data by: detecting atleast one packet identifier of packets within the extracted MPEGpackets; counting a number of packet identifiers associated with validdata; and determining that a ratio of the number of packet identifiersassociated with valid data to a number of packets extracted from theMPEG transport stream is greater than a predetermined threshold.
 15. Thetest instrument of claim 13, wherein the processor determines that theOOB content includes the predetermined amount of valid data by:detecting at least one packet identifier of packets within the extractedMPEG packets; counting a number of packet identifiers associated withvalid data; counting a number of packet identifiers associated withinvalid data; and determining that a ratio of the number of packetidentifiers associated with valid data to the number of packetidentifiers associated with invalid data is greater than a predeterminedthreshold.
 16. The test instrument of claim 11, wherein the OOB channeldata is transmitted using a stream of asynchronous transfer mode (ATM)cells formatted and modulated in accordance with a Society of Cable andTelecommunications Engineers (SCTE) 55-2 specification and the processordemodulates the captured OOB channel data by demodulating the stream ofATM cells to obtain a demodulated stream of ATM cells.
 17. The testinstrument of claim 16, wherein the processor extracts the OOB contentfrom the demodulated OOB channel data by: extracting ATM cells from thedemodulated stream of ATM cells.
 18. The test instrument of claim 17,wherein the processor determines that the OOB content includes thepredetermined amount of valid data by: counting a number of ATM cellscomprising data within the extracted ATM cells; and determining that aratio of the number of ATM cells comprising data to a number of ATMcells extracted from the stream of ATM cells is greater than apredetermined threshold.
 19. The test instrument of claim 17, whereinthe processor determines that the OOB content includes the predeterminedamount of valid data by: counting a number of ATM cells comprising datawithin the extracted ATM cells; counting a number of unassigned ATMcells within the extracted ATM cells; and determining that a ratio ofthe number of ATM cells comprising data to the number of unassigned ATMcells is greater than a predetermined threshold.
 20. The test instrumentof claim 11, wherein the processor is further configured to determinethat the OOB channel is not active in response to determining that theOOB content does not include the predetermined amount of valid data.